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Register a new userBulk electronic structure of the antiferromagnetic superconducting phase in ErNi2B2C
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We have performed temperature (T) - dependent laser-photoemission spectroscopy of antiferromagnetic (AF) superconductor ErNi2B2C to study the electronic-structure evolution reflecting the interplay between antiferromagnetism and superconductivity. The spectra at the superconducting (SC) phase show a very broad spectral shape. T-dependent SC gap shows a sudden deviation from the BCS prediction just below TN. This observation can be well explained by the theoretical model and thus represents characteristic bulk electronic structure of the AF SC phase for the first time.
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The point-contact (PC) spectra of the Andreev reflection dV/dI curves of the superconducting rare-earth nickel borocarbide ErNi2B2C (Tc=11 K) have been analyzed in the one-gap and two-gap approximations using the generalized Blonder-Tinkham-Klapwijk (GBTK) model and the Beloborodko (BB) model allowing for the pair-breaking effect of magnetic impurities. Experimental and calculated curves have been compared not only in shape, but in magnitude as well, which provide more reliable data for determining the temperature dependence of the energy gap (or superconducting order parameter) Delta(T). The anisotropic effect of antiferromagnetic ordering at T_N =6 K on the superconducting gap/order parameter has been determined: as the temperature is lowered, Delta(T) decreases by 25% in the c-direction and only by 4% in the ab-plane. It is found that the pair-breaking parameter increases in the vicinity of the magnetic transitions, the increase being more pronounced in the c-direction. The efficiency of the models was tested for providing Delta(T) data for ErNi2B2C from Andreev reflection spectra.
We report the experimental and theoretical study on magnetic nature of Bi3Ni system. The structure is found to be orthorhombic (Pnma) with lattice parameters a = 8.879{AA} b = 4.0998{AA} and c = 4.099{AA}. The title compound is synthesized via a solid state reaction route by quartz vacuum encapsulation of 5N purity stoichiometric ingredients of Ni and Bi. The superconducting transition temperature is found to be 4.1 K as confirmed from magnetization and specific heat measurements. The lower critical field (Hc1) and irreversibility field (Hirr) are around 150 and 3000Oe respectively at 2K. Upper critical field (Hc2) as determined from in field (up to 4 Tesla) ac susceptibility is found to be around 2 Tesla at 2K. The normal state specific heat is fitted using Sommerfeld-Debye equation C(T) = {gamma}T + {beta}T3+{delta}T5 and the parameters obtained are {gamma}= 11.08mJ/mol-K2, {beta}= 3.73mJ/mol-K4 and {delta}= 0.0140mJ/mol-K6. The calculated electronic density of states (DOS) at Fermi level N(EF) and Debye temperature {Theta}D are 4.697 states/eV per formula unit and 127.7K respectively. We also estimated the value of electron phonon coupling constant ({lambda}) to be 1.23, which when substituted in MacMillan equation gives Tc = 4.5K. Density functional (DFT) based calculations for experimentally determined lattice parameters show that Ni in this compound is non-magnetic and ferromagnetic interactions seem to play no role. The Stoner condition I*N(EF) = 0.136 per Ni atom also indicates that system cannot have any ferromagnetism. The fixed spin moment (FSM) calculations by fixing total magnetic moment on the unit cell also suggested that this system does not exhibit any signatures of ferromagnetism.
We study electronic properties of a superconducting topological insulator whose parent material is a topological insulator. We calculate the temperature dependence of the specific heat and spin susceptibility for four promising superconducting pairings proposed by L. Fu and E. Berg (Phys. Rev. Lett. 105, 097001). Since the line shapes of temperature dependence of specific heat are almost identical among three of the four pairings, it is difficult to identify them simply from the specific heat. On the other hand, we obtain wide varieties of the temperature dependence of spin susceptibility for each pairing reflecting the spin structure of Cooper pair. We propose that the pairing symmetry of superconducting topological insulator can be determined from measurement of Knight shift by changing the direction of applied magnetic field.
Here we present bulk property measurements and electronic structure calculations for PuFeAsO, an actinide analogue of the iron-based rare-earth superconductors RFeAsO. Magnetic susceptibility and heat capacity data suggest the occurrence of an antiferromagnetic transition at TN=50 K. No further anomalies have been observed down to 2 K, the minimum temperature that we have been able to achieve. Structural measurements indicate that PuFeAsO, with its more localized 5f electrons, bears a stronger resemblance to the RFeAsO compounds with larger R ions, than NpFeAsO does.
We present a soft X-ray angle-resolved photoemission spectroscopy (SX-ARPES) study of the stoichiometric pnictide superconductor LaRu2P2. The observed electronic structure is in good agreement with density functional theory (DFT) calculations. However, it is significantly different from its counterpart in high-temperature superconducting Fe-pnictides. In particular the bandwidth renormalization present in the Fe-pnictides (~2 - 3) is negligible in LaRu2P2 even though the mass enhancement is similar in both systems. Our results suggest that the superconductivity in LaRu2P2 has a different origin with respect to the iron pnictides. Finally we demonstrate that the increased probing depth of SX-ARPES, compared to the widely used ultraviolet ARPES, is essential in determining the bulk electronic structure in the experiment.
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